Many cryogenic refrigerators, such as Stirling refrigerators and pulse tubes, are driven by a reciprocating pressure wave. To generate the waves, state of the art practice employs clearance gap pistons driven by linear motors, which are both efficient but costly technologies.
A Stirling refrigerator achieves cooling by compressing the working gas in a compression space where heat is rejected, moving the compressed gas through a regenerator which cools it down, expanding the gas in an expansion space where heat is absorbed and finally moving the gas back through the regenerator to the compression space, the regenerator warming it up again. The Stirling machine typically has the expansion lagging compression by 90 degrees in the cycle. Typically Stirling refrigerators use two pistons, either positively driven or in a resonant condition 90 degrees out of phase.
Referring to FIG. 1, pulse tube refrigerators 10 can run the same gas cycle using a pressure wave generator 11, regenerator 12, and plug of gas in the pulse tube 13 as a virtual expansion piston thus eliminating moving parts in the cold part of the machine. An orifice or inertance tube 15 and reservoir 16 are used to achieve the required phase shift. The pulse tube also has a heat pumping effect so heat is rejected at 14 and a large temperature gradient along the pulse tube's length can be maintained. Heat exchanger 17 removes the heat of compression and heat exchanger 18 absorbs heat at the cold temperature.
It is an object of the present invention to provide an improved pressure wave generator for driving cryogenic refrigerator systems, or to at least provide the public with a useful choice.